1. Field of the Invention
The present invention relates to nonlinear optical thin-films utilized for optical switches, optical harmonic generators or the like, particularly to that having a semiconductive fine structure capable of exhibiting an extremely large optical nonlinearity.
2. Related Art
Conventionally, there has been known a semiconductor doped glass as a nonlinear optical material exhibiting a large nonlinearity.
FIG. 4 is a schematic cross-sectional view showing a fine structure of the conventional nonlinear optical thinfilm. As shown therein, this material is comprised of a glass matrix 1 and semiconductor ultra-fine particles 2 dispersed in the glass matrix. The optical nonlinearity of this material per a unit volume of the same is extremely large and it is reported that the optical nonlinearity amounts to about 200 times as large as that of a bulk crystal of the same semiconductor. Although reasons why such a large optical nonlinearity is obtained are not so clear, it is supposed that a quantum size effect contributes thereto which is caused for excitons (composite particles each comprised of an electron and a hole) generated in the semiconductor to be trapped in respective ultra-fine particles. However, it is very difficult to heighten the volume ratio of the ultra-fine particles up to about 1% since the semiconductor-doped glass is made by subjecting a homogeneous glass body containing components of the semiconductor to a heat treatment for crystallizing semiconductor ultra-fine particles. Due to this, the optical nonlinearity obtained actually is not so large in comparison with that of the bulk crystal. Further, since it is difficult to unify the shape and size of the ultra-fine particle and the crystallographic orientation, the actual nonlinearity is not so large as expected.